1. Field of the Invention
The present invention relates to a technology for forming a color filter used for a CCD camera, various display elements such as liquid crystal display elements, or a color sensor, and in particular relates to a method for manufacturing a colored layer or black matrix. More particularly, the present invention relates to a method for manufacturing a new color filter which simply forms such a colored layer or black matrix with high resolution.
2. Discussion of the Related Art
Currently, there are well-known methods for manufacturing a color filter include (1) dyeing, (2) pigment dispersion, (3) printing, (4) ink jet, (5) electrodeposition, and (6) micelle electrolysis.
Among these methods, both the dyeing and pigment dispersion methods listed above in (1) and (2) have reached a substantially complete level in terms of technology and have been used for many color solid-state image sensing devices (CCD). However, these two methods require patterning through a photolithography process, thus resulting in increased process steps at higher costs.
On the contrary, the printing and ink jet methods listed above in (3) and (4) do not require any photolithography process. However, the printing method listed above in (3), in which printing is performed on a thermosetting resin dispersed with pigment and then the resin is cured, is inferior in resolution and uniformity of film thickness. The ink jet method listed above in (4), in which a color filter layer is obtained by forming a particular ink recipient layer, making hydrophilic/hydrophobic portions on its surface through an appropriate process, and then discharging an ink onto the hydrophilic portions, has several problems with resolution and positioning accuracy because it may be more likely that an adjacent filter layer will be improperly colored.
In the electrodeposition method listed above in (5), a color filter layer of R.G.B. is obtained by repeating three times an electropainting process in which a high voltage of approximately 70 V is applied to a previously patterned transparent electrode in an electrolytic solution of water-soluble polymer dispersed with pigment to form an electrodeposition film. This method has disadvantages that patterning is limited to particular shapes and it cannot be used for TFT liquid crystal displays because the transparent electrode must have been previously patterned through a photolithography process for use as an electrode for electrodeposition. No additional patterning would be required if a color filter could be formed integrally with pixel electrodes of a TFT liquid crystal substrate through electrodeposition. However, since a prior electrodeposition method used higher electrodeposition voltages, it was very difficult to cause an active-matrix circuit to produce electrodeposits on transparent pixel electrodes and electrodeposition could not be performed using TFT pixel electrodes.
The micelle electrolysis method listed above in (6) is a kind of electrodeposition but oxidation-reduction reaction of ferrocene used as a deposition material allows the electrodeposition voltage to be reduced and a color filter can be integrally formed on a TFT liquid crystal substrate through electrodeposition. However, since a TFT has a larger internal resistance, some voltage can be applied to it but a large current cannot flow through it. Therefore, it is very difficult to form a color filter directly on pixel electrodes through a TFT drive circuit even if the micelle electrolysis method is used. In addition, a thin film formed through the micelle electrolysis method may contain as impurities ferrocene or a surface-active agent, which is essential to the film forming process but may be incorporated into the film during deposition, and thus, the formed color filter may have decreased transparency. This method has further disadvantages that the manufacturing efficiency will be decreased because it may take several tens minutes to perform electrodeposition and that it requires a higher cost because a ferrocene compound, which is a required component for the electrolytic solution, is very expensive. Moreover, any alkali metal that is required as a supporting salt cannot be used because it may adversely affect a TFT circuit or liquid crystal.
Japanese Patent Laid-Open No. 5-5874 (1993) proposes a method for integrally forming a color filter on a TFT substrate. According to this method, a color filter layer with predetermined pixels of predetermined colors is formed through electrodeposition using a TFT drive circuit. Therefore, this method requires an electrodeposition apparatus and the TFT has a very large internal resistance which may cause voltage drop to prevent a necessary current or voltage from being produced for electrodeposition, and thus, additional electrodes for electrodeposition may be required. In addition, the TFT circuit must be protected against an alkali metal contained in the film and the electrodeposition method requires an electrodeposition solution of higher conductivity and addition of a supporting salt, which may contribute to incorporation of impurities as described above. Moreover, since no typical TFT drive circuit can be used to perform electrodeposition directly on pixel electrodes, another type of TFT is required which has a small internal resistance to allow a high current to flow through it. From these reasons, such a usual electrodeposition technology might be considered very difficult to fabricate a color filter using a TFT drive circuit. Thus, no liquid crystal display element of practical level could be implemented by integrally forming a color filter substrate and a TFT substrate. Japanese Patent Laid-Open No. 59-90818 (1984) describes a method for manufacturing a color filter, comprising the steps of: providing on a transparent substrate electrodes consisting of a conductive transparent thin film divided into a plurality of regions; selecting each electrode and applying a voltage to it for electropainting; and repeating the previous steps to color different electrodes with different colors, and the specification also describes that the method is applicable to switching elements such as TFTs. Japanese Patent Laid-Open No. 60-23834 (1985) describes a method for manufacturing a matrix-type multicolor display device which comprises a plurality of gate lines and a plurality of source lines orthogonal to the gate lines with a thin film transistor array formed at each intersection therebetween, which has a substrate with a display electrode comprising a color filter of a plurality of tones and the drain of the thin film transistor connected thereto and an opposed substrate with an overall conductor formed thereon, and which has a display material sandwiched between the transistor array and the transparent conductor, including the steps of: using conductive portions of the color filter and the transistor array as electrodeposition electrodes; selectively forming a colored film on these conductive portions through electrodeposition in a solution which contains at least electrodeposition polymers and colorants dissolved or dispersed therein; and repeating the previous steps. Japanese Patent Laid-Open No. 2-24603 (1990) describes a method for manufacturing a color filter in obtaining a color filter which has a transparent electrode formed on a transparent substrate according to a predetermined pattern and has an organic pigment layer on the transparent electrode, including the steps of: immersing the substrate and an electrolytic electrode in a solution which contains a non-water-soluble organic pigment solubilized in a micelle solution of a surface-active agent; producing a current flow between the predetermined pattern of the transparent electrode and the electrolytic electrode to cause micelle electrode oxidation on the transparent electrode to deposit organic pigment molecules on the transparent electrode; and repeating the previous steps on other transparent electrode patterns with other organic pigments having different spectral characteristics.
On the other hand, a well-known method for forming a film through optical reaction is the Photocatalytic Deposition Method, which is a kind of micelle electrolysis, and devised by Hoshino of Chiba University. The Photocatalytic Deposition Method is described in detail by Hoshino, Kato, Kurasako, and Kokado in a publication of The Society of Photographic Science and Technology of Japan, Vol. 59, No. 2 (1996). The method uses oxidation-reduction reaction of ferrocene to deposit a film on an unilluminated region but it has disadvantages that it requires application of voltage from an external device, resulting in a complicated apparatus to be used for the method. Therefore, it is unsuitable for forming fine patterns such as color filters.
The present invention has been made in view of the above circumstances and provides a method for manufacturing a TFT-integrated color filter, which can controllably fabricate a color filter having a high aperture efficiency and a high resolution at low costs without the need for aligning the color filter with a TFT substrate as required by the prior art.
The method for manufacturing the TFT-integrated color filter can be attained by providing a method for manufacturing a color filter and an electrolytic solution therefor as follows:
(1) A method for manufacturing a thin-film transistor integrated color filter is provided, including the steps of: preparing a color filter fabrication substrate by forming thin-film transistors and light-transmissive pixel electrodes in arrays on a light-transmissive substrate and providing a photocatalytic thin film in contact with the pixel electrodes so that portions of the pixel electrodes are exposed; preparing an electrolytic solution containing a coloring material and another material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH; placing the color filter fabrication substrate in the electrolytic solution so that at least the pixel electrodes and the photocatalytic thin film are in contact with the electrolytic solution, and with predetermined ones of the thin-film transistors driven selectively; and illuminating the color filter fabrication substrate with ultraviolet light to form a colored film on the surface of the photocatalytic thin film corresponding to the undriven thin-film transistors.
The method for manufacturing a color filter according to the present invention can controllably fabricate a color filter having a high aperture efficiency and a high resolution at low costs without the need for aligning the color filter with a TFT substrate as required by the prior art because the color filter is formed integrally with the TFT. Therefore, a high-precision liquid crystal display element can be manufactured at low costs by using the color filter.
(2) A method for manufacturing a thin-film transistor integrated color filter is provided, including the steps of: preparing a color filter fabrication substrate by forming thin-film transistors and light-transmissive pixel electrodes in arrays on a light-transmissive substrate and providing a photocatalytic thin film in contact with the pixel electrodes so that portions of the pixel electrodes are exposed; preparing an electrolytic solution containing a coloring material and another material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH; placing the color filter fabrication substrate in the electrolytic solution so that at least the pixel electrodes and the photocatalytic thin film are in contact with the electrolytic solution, with predetermined ones of the thin-film transistors driven selectively; illuminating the color filter fabrication substrate with ultraviolet light to form a colored film on the surface of the photocatalytic thin film corresponding to the undriven thin-film transistors; and repeating the previous steps at one or more times with another electrolytic solution containing another coloring material of a different color.
(3) The method for manufacturing a color filter according to the paragraph (1) or (2) above is provided, wherein the photocatalytic thin film is a thin film containing titanium oxide.
(4) The method for manufacturing a color filter according to any one of the paragraphs (1) through (3) above is provided, wherein the material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH has a carboxyl in the molecule.
(5) The method for manufacturing a color filter according to any one of the paragraphs (1) through (4) above is provided, wherein the material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH is a polymer material.
(6) The method for manufacturing a color filter according to any one of the paragraphs (1) through (5) above is provided, wherein the polymer material is a copolymer of a monomer having hydrophobic groups and hydrophilic groups and the ratio of the number of hydrophobic groups to the total number of hydrophobic and hydrophilic groups is within the range from 40% to 80%.
(7) The method for manufacturing a color filter according to any one of the paragraphs (1) through (6) above is provided, wherein the pH of the electrolytic solution is controlled by a pH adjuster which may not affect the film-deposition characteristics.
(8) The method for manufacturing a color filter according to any one of the paragraphs (1) through (7) above is provided, wherein the conductivity of the electrolytic solution is controlled by a salt which may not affect the film-deposition characteristics.
(9) The method for manufacturing a color filter according to any one of the paragraphs (1) through (8) above is provided, wherein the temperature of the electrolytic solution is controlled.
(10) The method for manufacturing a color filter according to any one of the paragraphs (1) through (9) above is provided, wherein the electrolytic solution contains light-transmissive and conductive particulates.
(11) The method for manufacturing a color filter according to any one of the paragraphs (1) through (10) above is provided, wherein after the colored film is formed, a black matrix is formed by applying a black ultraviolet-curing resin to the surface on which the colored film is formed, illuminating the light-transmissive substrate with ultraviolet light from the side with no colored film, and removing non-curing portions.
(12) A method for manufacturing a thin-film transistor integrated color filter is provided, including the steps of: preparing a color filter fabrication substrate with a black matrix by forming thin-film transistors and light-transmissive pixel electrodes in arrays on a light-transmissive substrate; applying a black positive-working photoresist thereto; illuminating the substrate with light from the side with no thin-film transistors nor light-transmissive pixel electrodes; removing the positive-working photoresist from the illuminated region; and providing a photocatalytic thin film in contact with the pixel electrodes so that portions of the pixel electrodes are exposed, preparing an electrolytic solution containing a coloring material and another material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH, placing the color filter fabrication substrate in the electrolytic solution so that at least the pixel electrodes and the photocatalytic thin film are in contact with the electrolytic solution, with predetermined ones of the thin-film transistors driven selectively, illuminating the color filter fabrication substrate with ultraviolet light to form a colored film on the surface of the photocatalytic thin film corresponding to the undriven thin-film transistors, and repeating the previous steps at one or more times with another electrolytic solution containing another coloring material of a different color.
(13) The method for manufacturing a color filter according to any one of the paragraphs (1) through (10) above is provided, wherein a black matrix is formed in a light-transmissive region with no colored film by applying a black negative-working photoresist to the color filter fabrication substrate after the colored film is formed, illuminating the substrate with light from the side with no colored film, and removing the negative-working photoresist.
(14) The method for manufacturing a color filter according to any one of the paragraphs (1) through (10) above is provided, wherein the gate electrode and the drain electrode of each thin-film transistor are made of a low-reflection material to provide the electrodes with similar functions to those of the black matrix.
(15) The method for manufacturing a color filter according to the paragraph (14) above is provided, wherein the gate electrode and the drain electrode are made of two or three layers of Cr.
(16) The method for manufacturing a color filter according to any one of the paragraphs (1) through (15) above is provided, wherein a light-transmissive conductive thin film is formed on the colored film for continuity with the pixel electrodes.
(17) An electrolytic solution used for the method for manufacturing a color filter according to any one of the paragraphs (1) through (16) above is provided, wherein it contains a coloring material and another material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH.
(18) The electrolytic solution according to the paragraph (17) above is provided, wherein the material which may decrease in solubility or dispersibility with respect to an aqueous solution with any change in pH is a polymer material having a carboxyl and the coloring material is a pigment.
(19) The electrolytic solution according to the paragraph (17) or (18) above is provided, wherein the polymer material is a copolymer of a monomer having hydrophobic groups and hydrophilic groups and the ratio of the number of hydrophobic groups to the total number of hydrophobic and hydrophilic groups is within the range from 40% to 80%.
(20) A method for manufacturing a thin-film transistor integrated color filter is provided, including the steps of: preparing a color filter fabrication substrate by forming thin-film transistors and light-transmissive pixel electrodes in arrays on a light-transmissive substrate and providing a photocatalytic thin film in contact with the pixel electrodes so that portions of the pixel electrodes are exposed; preparing an electrolytic solution containing a coloring material and another material which has a nature that it deposits in a film through a photocatalytic reaction; placing the color filter fabrication substrate in the electrolytic solution so that at least the pixel electrodes and the photocatalytic thin film are in contact with the electrolytic solution, and with predetermined ones of the thin-film transistors driven selectively; illuminating the color filter fabrication substrate with ultraviolet light to form a colored film on the surface of the photocatalytic thin film corresponding to the undriven thin-film transistors.
(21) A method for manufacturing a thin-film transistor integrated color filter is provided, including the steps of: preparing a color filter fabrication substrate by forming thin-film transistors and light-transmissive pixel electrodes in arrays on a light-transmissive substrate and providing a photocatalytic thin film in contact with the pixel electrodes so that portions of the pixel electrodes are exposed; preparing an electrolytic solution containing a coloring material and another material which has a nature that it deposits in a film through a photocatalytic reaction; placing the color filter fabrication substrate in the electrolytic solution so that at least the pixel electrodes and the photocatalytic thin film are in contact with the electrolytic solution, with predetermined ones of the thin-film transistors driven selectively; illuminating the color filter fabrication substrate with ultraviolet light to form a colored film on the surface of the photocatalytic thin film corresponding to the undriven thin-film transistors; and repeating the previous steps at one or more times with another electrolytic solution containing another coloring material of a different color.
(22) A color filter which has thin-film transistors, pixel electrodes, and a colored film formed on a light-transmissive substrate is provided, wherein a photocatalytic thin film is provided in contact with the pixel electrodes so that portions of the pixel electrodes are exposed and the colored film is formed on the photocatalytic thin film.
(23) A liquid crystal display is provided, which has at least a color filter according to the paragraph (22) above, an opposed substrate placed to be opposed to the color filter, and a liquid crystal material sandwiched between the color filter and the opposed substrate.